The present disclosure relates to a semiconductor integrated circuit, and more particularly relates to a semiconductor integrated circuit which transmits and receives data to and from an external memory.
Power consumption of semiconductor integrated circuits tends to increase in recent years with improvement of their performance and processing speeds. On the other hand, there are increasing demands for reducing their power dissipation.
In general, the power dissipation of a semiconductor integrated circuit can be reduced by dynamic control of a voltage supplied to an internal circuit of the semiconductor integrated circuit.
However, when a dynamic change is made to a supply voltage supplied to an interface (IF) circuit serving as an internal circuit and performing a data transmission/reception operation with an external memory, an alternate current (AC) timing specification between the external memory and the IF circuit is no longer met, which may disable access to the memory.
Japanese Patent No. 4465539 discloses a configuration for a memory control system. In this system, if a change is made to the configuration or operating frequency of a memory, a memory access test automatically starts without a wait at a minimum voltage in starting the system.
In this configuration, if access to the memory cannot be done through the memory access test, the memory access test is retried with the supply voltage raised. If the memory access is done this time, the voltage at that time is determined to be a minimum operating supply voltage. However, if it is still difficult to get the memory access done even when the supply voltage is set to be the maximum value, a wait is inserted and the number of waits is increased on a clock-by-clock basis before the memory access test is retried. Repeating the memory access test in this manner minimizes the number of waits inserted in the memory access. Further, since the supply voltage used during actual memory access is determined to be the minimum required one, the memory access can be speeded up with the power dissipation cut down.